feat: add benchmarks for encoding

[zealchen]

Rationale

#1600

Detailed Changes

Additional benchmarks for this issue

Test Plan

Append 100 new delta sstfiles to snapshot with 1000 records.

Benchmarking bench_encoding/new_format_encoding/0: Collecting 10 samples in estimated 5.0005 s (494k iterations)
bench_encoding/new_format_encoding/0
                        time:   [10.232 µs 10.611 µs 10.900 µs]
                        change: [-1.5176% +2.1745% +5.9315%] (p = 0.30 > 0.05)
                        No change in performance detected.

[jiacai2050]

LGTM